1964 Volume 8 Issue 3 Pages 235-244
The pupa of the Asiatic common looper, Autographa nigrisigna WALKER, shows colour diversity dependent on temperature; it becomes deep black in colour when reared at 20°C or lower, yellowish brown when reared at 30°C, and intermediate coloured when reared at 25°C.
1) As a result of experiments in which temperature was reversed at various stages of development, it is found that the pupal colour is determined by the environmental temperature received during the period ranging from the middle stage of the larval period to hardening of the pupal cuticle after pupation. The temperature received before this period has no influence upon the pupal colour.
2) When the temperature conditions change at the beginning of the last (5th) instar period or prior to it, the pupal colour was largely affected by the temperature after the changing, regardless of the temperature sequence; low (18°C) to high (30°C) or high to low.
3) In cases of changing the temperatures at various age of the last instar period, the effect of the second temperature was far more remarkable when the change is made from low to high. In general, this high temperature after the low strongly eliminated the effects of the preceding low temperature. The low temperature after high was less effective for producing high percentage of intermediate-type pupae due to the incomplete eliminating effect of the preceding high temperature. The colour grade of intermediate-type pupae obtained by this experiment varied with the mode of temperature changing.
4) Wing pattern, wing shape or other characters of the adults of Autographa nigrisigna showed no appreciable difference between those emerged from black-type and yellowish brown-type pupae.
5) When the insects were ligated between the 2nd and the 3rd abdominal segments at early prepupal period at which the temperature was changed from high (30°C) to low (18°C), the pupal cuticles were melanized only in the part anterior to the ligature. In the same series of experiment where the temperature reversal was made from low to high, however, the pupal cuticles were yellowish brown without black spots in both anterior and posterior parts. It is considered that the centre of response to low temperature may exist in some part anterior to the 2nd abdominal segment of the larval body, and that the transmission of some factor towards the posterior part may be prevented by ligation. It seems that this factor is of endocrine nature. When the temperature changed from low to high, the reaction of melanization is supposed to be suppressed in every part of the body directly by high temperature following ligation, since it was possible that the darkening reaction was already progressing in both parts prior to the time of temperature reversal.
6) Although there were some differences in the actual range of colour grade among species, the fourteen species of Plusiinae so far examined showed the similar tendency of the pupal colour response to temperature as Autographa nigrisigna, that is, the melanization of the cuticle increased under low temperature and reduced under high temperature.
